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scott2000 said:
arrgh... I had that happen once....Nice pair of smoked glass 6sn7s the seller taped together  and in my excitement I separated them with too much force  and one shot off to the tile floor...

Hopefully your close.... I've read the tolerances can be as much as 20% in this thing so maybe...

That's the worst! This unfortunately was a very nice NOS RCA so I feel you. I'm replacing it with an EH. This circuit doesn't really need super nice tubes and I like EH tubes in general. They're fine.
 
FarisElek said:
That's the worst! This unfortunately was a very nice NOS RCA so I feel you. I'm replacing it with an EH. This circuit doesn't really need super nice tubes and I like EH tubes in general. They're fine.

I've got all RCA tubes throughout, but I saw the EH 12BH7 and it sparked my interest - for some reason I am drawn to the reliability of new production tubes - but perhaps it is just an illusion I am buying into and they aren't any more reliable than the used/vintage on ebay.

I tested an EH 6922 in a Rode NTK once upon a time. The top end was extended, or open rather, and the low end was deep and slightly bloated in that circuit. Would have been awesome for recording bass. I settled on a new production Genelex Gold Lion 6922 after testing a rather noisy Amperex 6DJ8 and the Gold Lion was so close in dimension and freq response (only without the noise) it just made sense.

Is there anywhere I can find subjective notes on different tubes in the LA2A? Part of me wan't to do a video on different 12BH7 and 12AX7 brands in the LA2A.
 
justinheronmusic said:
I've got all RCA tubes throughout, but I saw the EH 12BH7 and it sparked my interest - for some reason I am drawn to the reliability of new production tubes - but perhaps it is just an illusion I am buying into and they aren't any more reliable than the used/vintage on ebay.

I tested an EH 6922 in a Rode NTK once upon a time. The top end was extended, or open rather, and the low end was deep and slightly bloated in that circuit. Would have been awesome for recording bass. I settled on a new production Genelex Gold Lion 6922 after testing a rather noisy Amperex 6DJ8 and the Gold Lion was so close in dimension and freq response (only without the noise) it just made sense.

Is there anywhere I can find subjective notes on different tubes in the LA2A? Part of me wan't to do a video on different 12BH7 and 12AX7 brands in the LA2A.

Depends on the circuit and the tubes used in it. U67 is really sensitive to the type of EF86 it has in it, but you can use pretty much anything for the gain 12ax7 in the LA2A and it will sound pretty much the same. I believe it has to do with negative feedback. I've messed with the LA2A circuit before and the biggest difference I heard was playing with the output capacitor and using a good quality t4b. I'm sure you could run some sweeps and see for yourself. It's difficult to do that with microphones but pretty easy to do with line level gear.

 
FarisElek said:
Depends on the circuit and the tubes used in it. U67 is really sensitive to the type of EF86 it has in it, but you can use pretty much anything for the gain 12ax7 in the LA2A and it will sound pretty much the same. I believe it has to do with negative feedback. I've messed with the LA2A circuit before and the biggest difference I heard was playing with the output capacitor and using a good quality t4b. I'm sure you could run some sweeps and see for yourself, or maybe prove me wrong. It's difficult to do that with microphones but pretty easy to do with line level gear.
 
justinheronmusic said:
Wow, not even the input transformer?

Transformers probably do too. By how much I couldn't say. I'd imagine if they're good transformers they'll sound good though. I know there is a common Jensen mod for the LA2A which uses different impedence at the input I believe. That probably changes things more than swapping between several different good transformers of the same ratio. I'm not an expert though. Who knows?
 
Okay, finished my point to point build of the LA2a. All voltages appear to be within 20% or less except pin 8 of V1, which has nothing.

Gain is working just fine EXCEPT, for the loud buzz which is louder than the gain. Also, no low end. Using edcor transformers. I didn't load these any particular way, I just followed the recpro layout.

The buzz is probably the heater wiring. I'm going to make sure it's really tighly sound and not touching a bunch of other wires later. I'll follow the path of pin 8 and see if u can fix whatever is preventing it from being the right voltage. If anyone can enlighten me on what might cause no low end and how in supposed to terminate the war transformers I don't know much about termination in general.

Ryan
 
Just curious, how are people physically mounting C14 (the variable cap near the output tx) on their units?

I've got some of the Arco 465 caps, but I can't find any pics showing how they're actually mounted on the rear panel. I was gonna go with insulated standoffs, with the cap terminals and other components (C6, R30) screwed onto the standoffs using ground lug washers, but I figured I'd check here to see what other people are doing before I do anything.
 
Just curious, how are people physically mounting C14 (the variable cap near the output tx) on their units?

I've got some of the Arco 465 caps, but I can't find any pics showing how they're actually mounted on the rear panel. I was gonna go with insulated standoffs, with the cap terminals and other components (C6, R30) screwed onto the standoffs using ground lug washers, but I figured I'd check here to see what other people are doing before I do anything.
https://groupdiy.com/threads/la2a-variable-capacitors.66652/post-844930
 
So the consensus is just forget the Arco caps for that position and use a fixed 150pf instead?

That actually makes things less straightforward tbh, as it involves ordering parts I don't have (150pf caps) and using them in place of parts that I already own.
 
Just curious, how are people physically mounting C14 (the variable cap near the output tx) on their units?

I've got some of the Arco 465 caps, but I can't find any pics showing how they're actually mounted on the rear panel. I was gonna go with insulated standoffs, with the cap terminals and other components (C6, R30) screwed onto the standoffs using ground lug washers, but I figured I'd check here to see what other people are doing before I do anything.
I put a bunch of pics in my fun build thread (that I don't know if I finished, but the led meter is all in) I think I showed how to add the variable caps
https://groupdiy.com/threads/sinatra-sings-my-way-scratch-la2a-build.65716/page-2
 
Just curious, how are people physically mounting C14 (the variable cap near the output tx) on their units?

I've got some of the Arco 465 caps, but I can't find any pics showing how they're actually mounted on the rear panel. I was gonna go with insulated standoffs, with the cap terminals and other components (C6, R30) screwed onto the standoffs using ground lug washers, but I figured I'd check here to see what other people are doing before I do anything.
I put a bunch of pics in my fun build thread (that I don't know if I finished, but the led meter is all in) I think I showed how to add the variable caps
https://groupdiy.com/threads/sinatra-sings-my-way-scratch-la2a-build.65716/page-2
 
Hallo zusammen,
Dies ist mein erster Beitrag überhaupt.

Ich brauche Hilfe

Ich habe gerade mein Dual LA2A mit Drip Opto7 platinenset fertiggestellt, und es funktioniert bis jetzt sehr gut. Das Problem, das ich habe, ist ein Summen oder Brummen bei ca. 90 Hz @ - 48 dbfs. This Brummen wird nicht beeinflusst durch das Gain oder die Peak Reduction Potis an der Front. Glaube auch nicht das es ein Erdungsproblem ist, könnte mich auch irren.
Hatt jemand eine Idee oder einen Hinweis wo ich suchen soll!!!

Danke für jede Antwort

LG Cream
 
Hallo zusammen,
Dies ist mein erster Beitrag überhaupt.

Ich brauche Hilfe

Ich habe gerade mein Dual LA2A mit Drip Opto7 platinenset fertiggestellt, und es funktioniert bis jetzt sehr gut. Das Problem, das ich habe, ist ein Summen oder Brummen bei ca. 90 Hz @ - 48 dbfs. This Brummen wird nicht beeinflusst durch das Gain oder die Peak Reduction Potis an der Front. Glaube auch nicht das es ein Erdungsproblem ist, könnte mich auch irren.
Hatt jemand eine Idee oder einen Hinweis wo ich suchen soll!!!

Danke für jede Antwort

LG Cream
Hallo Cream, bitte nur in Englisch posten. Es ist auch eine gute Idee die Schaltpläne zum Drip Opto7 Platinenset gleich mit zu posten, da diese wahrscheinlich zahlreiche Modifikationen zum Original beinhalten. So kann man dir besser helfen. Danke!

Ps: Fotos des Aufbaus wäre auch gut...
 
Last edited:
Hi everyone, I just finished my Dual LA2A Opto7 from Drip Electronics. Everything works very well so far. Unfortunately I have a static 90 Hz hum at - 48 dBFs at the output on both channels !! When I turn up my Gain or Peak Reduction the Hum doesn't get touched by that. I have no idea where that can come from. !!!IMG_20210831_224703.jpg My 12AX7 and 12BH7 are matched pairs from Electro Harmonics. I installed Lundahl ll5402 as a transformer for the input and Lundahl ll1922 at the output. My T4bs are from IGS.
IMG_20210831_224625.jpg
IMG_20210831_224906.jpgIMG_20210831_225041.jpgIMG_20210831_225122.jpgIMG_20210831_225212.jpgIMG_20210831_225952.jpg

Does anybody have any Idear!
Thanks for Help and comments.
 
Hi Creamman,

first I have to say that I don't know this project from Drip or have built it myself before.

I have the following ideas and questions.

You write in your first post, that from your point of view, it is not a grounding problem. I think that is exactly what we have here.

The 90Hz you measured is most likely 100Hz since we both live in a 50Hz country. That and the fact that the hum is independent of the gain and other settings suggests that you have a groudloop somewhere. That happens very easily in such a complex project.

Therefore rule number 1: Each point of the circuit must have only one way to ground! Check this again. This happens often at the xlr jacks or the mounting of the PCB via the housing, provided that this PCB is error-free and has not already integrated this in the (signal) routing.

Since your hum is equally present on both channels, you should also take a closer look at the power supplies and the transformer.

When I compare your setup/the PCB with the schematics, it is noticeable that many things are not mentioned in the schematics. Are there more schematics of the Drip PSUs? How is the DC heating realized? Is the heater voltage referenced to B+? Elevated heater? Which transformer? 2 windings for the heater? How are the relays powered? Is there a central ground point? How is the protective earth connected?

Again, check for ground loops here, each part of the circuit may only have one path to ground. Are all voltages correct? Do you have a proper oscilloscope with which you can check the individual voltages?

Good luck!
 
Last edited:
Hi Creamman,

first I have to say that I don't know this project from Drip or have built it myself before.

I have the following ideas and questions.

You write in your first post, that from your point of view, it is not a grounding problem. I think that is exactly what we have here.

The 90Hz you measured is most likely 100Hz since we both live in a 50Hz country. That and the fact that the hum is independent of the gain and other settings suggests that you have a groudloop somewhere. That happens very easily in such a complex project.

Therefore rule number 1: Each point of the circuit must have only one way to ground! Check this again. This happens often at the xlr jacks or the mounting of the PCB via the housing, provided that this PCB is error-free and has not already integrated this in the (signal) routing.

Since your hum is equally present on both channels, you should also take a closer look at the power supplies and the transformer.

When I compare your setup/the PCB with the schematics, it is noticeable that many things are not mentioned in the schematics. Are there more schematics of the Drip PSUs? How is the DC heating realized? Is the heater voltage referenced to B+? Elevated heater? Which transformer? 2 windings for the heater? How are the relays powered? Is there a central ground point? How is the protective earth connected?

Again, check for ground loops here, each part of the circuit may only have one path to ground. Are all voltages correct? Do you have a proper oscilloscope with which you can check the individual voltages?

Good luck!
Thanks for your Answer.
Here is a Link to all the Informations of Drips Opto7 if you want to take a look at it...
https://www.google.com/url?sa=t&sou...Vaw11PHbcAj36G1J6H-GCogxa&cshid=1630649201613

I will check all Groundings again... But this will be next week because I have to work the hole Weekend.
I will let you know what's going on as soon as possible.

Have a nice weekend :)
 

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